Yanghui Sun

Lateral Etching of Core–Shell Au@Metal Nanorods to Metal-Tipped Au Nanorods with Improved Catalytic Activity

Selective growth/etching of hybrid materials is very important for the rational synthesis of hierarchical structures and precise modulation of their physical properties. Here, the lateral etching of the core-shell Au@Ag nanorods is achieved by FeCl(3) at room temperature, producing a number of dumbbell-like Ag-tipped Au nanorods. This selective etching at the side of the core-shell nanorods is attributed to the increased reactivity of the side facets, due to less surface passivation of cetyltrimethylammonium bromide. The similar synthetic strategy has also been demonstrated to be successful for the Pd-tipped Au nanorods that have not been reported before, indicating the great potential of this selective etching. The Ag-tipped Au nanorods are examined as a catalyst for the reduction of p-nitrophenol at room temperature. The Ag-tipped Au nanorods exhibit a higher catalytic activity than Au nanorods and core-shell Au@Ag nanorods, which could be attributed to the electronic effect and the unique structure in the Ag-tipped Au nanorods.

Compensation mechanism in N-doped ZnO nanowires.

N-doped ZnO nanowires are synthesized at a relatively low growth temperature of 500 degrees C by directly heating zinc powder using NH(3) as the dopant. The incorporation of N into the ZnO nanowires is experimentally confirmed by x-ray photoelectron spectroscopy, Raman spectra and photoluminescence measurements. By combining post annealing experiments after growth with first-principles calculations, the detailed migration mechanism of N and compensation mechanism in N-doped ZnO nanowires are systematically studied. The larger aspect ratio of nanowires favors the formation of oxygen vacancy and out-diffusion of substitutional N (N(O)), making N(O) in ZnO nanowires always compensated by hydrogen interstitials (H(I)). Our results can help to explain the challenge in getting p-type ZnO and shed new light on the possible realization of p-type doping of ZnO in the future.

In situ observation of ZnO nanowire growth on zinc film in environmental scanning electron microscope

In situ uniform growth of ZnO nanowires was realized and monitored at real time by heating zinc film in an environmental scanning electron microscope. Better controllability and repeatability were obtained by using zinc film as source material compared to traditionally used zinc powder. Morphology of the as-grown ZnO nanowires was found to depend on both the growth temperature and holding time. Low temperature (500 degrees C) and short growth time (approximately 20 min) favor one-dimensional nanowire growth, whereas longer holding time (>40 min) or higher temperature (700 degrees C) lead to nanosheet growth. The results suggest that the zinc vapor partial pressure is vital in determining the final morphology. These results help to give more insights into the mechanism of ZnO nanowire synthesis.

A Novel Way for Synthesizing Phosphorus-Doped Zno Nanowires

We developed a novel approach to synthesize phosphorus (P)-doped ZnO nanowires by directly decomposing zinc phosphate powder. The samples were demonstrated to be P-doped ZnO nanowires by using scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction spectra, X-ray photoelectron spectroscopy, energy dispersive spectrum, Raman spectra and photoluminescence measurements. The chemical state of P was investigated by electron energy loss spectroscopy (EELS) analyses in individual ZnO nanowires. P was found to substitute at oxygen sites (PO), with the presence of anti-site P on Zn sites (PZn). P-doped ZnO nanowires were high resistance and the related P-doping mechanism was discussed by combining EELS results with electrical measurements, structure characterization and photoluminescence measurements. Our method provides an efficient way of synthesizing P-doped ZnO nanowires and the results help to understand the P-doping mechanism.

Facile synthesis, optical properties and growth mechanism of elongated Mn-doped ZnSe1−xSx nanocrystals

Transition-metal doping in semiconductors is an important way to modulate their intrinsic properties or bring out new functionalities for applications. Here, elongated Mn-doped ZnSe1−xSx nanocrystals are synthesized through a facile one-pot reaction under mild conditions. These ZnSe1−xSx nanocrystals with a diameter of 2–4 nm have a cubic phase structure. EPR and PL spectra confirm the successful doping of Mn2+ into the ZnSe1−xSx nanocrystals, based on the corresponding hyperfine splitting constants and emission bands. The temporal evolution of UV-vis absorption and PL spectra indicates the growth-doping mechanism for the formation of the doped nanocrystals. Surface coating of these nanocrystals with a shell increases the quantum yield up to 35%. And the dual-function role of 1-dodecanethiol is confirmed in the formation of the elongated Mn-doped ZnSe1−xSx nanocrystals.

Growth mechanism study viain situ epitaxial growth of high-oriented ZnO nanowires

In situ epitaxial growth of high-oriented ZnO nanowires on annealed zinc film was realized in an environmental scanning electron microscope. Energy dispersive spectra, X-ray diffraction and photoluminescence measurements demonstrated that a thin layer of [001] ZnO was formed on the surface of zinc film after annealing. Formation of a ZnO layer on annealed zinc film caused dense [001] oriented nanowires compared to the sparse random nanowires grown on unannealed zinc film. Possible growth mechanism for the nanowires grown on annealed and unannealed film was discussed. This work offers a novel approach for effective epitaxial growth of high-oriented ZnO nanowires and helps to understand the growth mechanism of ZnO nanowires.

In situ growth and density-functional-theory study of polarity-dependent homo-epitaxial ZnO microwires

Polarity-dependent homo-epitaxy on (0001)-Zn and (000)-O surfaces of cleaved ZnO microwires was investigated by in situgrowth in ESEM and DFT simulations. ZnO monomers adsorption, adatoms desorption and chemisorption were simulated to understand the explicit mechanism.